Multiplex receiving circuit arrangement



- Oct. 22, 1940. A..KAHN 1 2,218,914

MULTIPLEX RECEIVING CIRCUIT ARRANGEMENT Filed Nov. 30, 1958 J AMPLIFIER & DETECTOR RECQlF/ER r0 CHANNEL 2 LOCK/N6 CIRCUIT CHANNEL 1} +55 Ec UT/L/ZA T/cw MEANS ..5b-I-+Ec INVENTOR ALF/{ED K N BY ATTORNEY LOCK/N6 cmcu/r 1 38 Patented Oct. 22, 1940 UNITED STATES MULTIPLEX RECEIVING CIRCUIT ARRANGEMENT Alfred Kahn, Ozone Park, N. Y., asslgnor to Radio Corporation of America, a corporation of Dela- Application November 30, 1938, Serial No. 243,131

4 Claims.

This invention relates to multiplex telegraph receiving systems and more particularly to a circuit arrangement adapted to feed into a locking circuit. It is a principal object of my invention 5 to provide a resistance coupled input circuit interconnecting the input lines of a telegraph receiver with a so-called locking circuit and utilization means by which multiplex telegraph signals of short duration are caused to be prolonged sufliciently for the operation of conventional receiving devices.

A further object of my invention is to provide a method of and apparatus for easily and emciently assigning the received signals to the different channels.

A still further object of my invention is to provide circuit arrangements in a receiving sys- ,tem such as shall be simple in construction, easy to maintain and made of the fewest possible elements in combination.

' The present invention is an improvement upon and an outgrowth from the invention covered by my Patent 1,995,181, which was issued March 19, 1935, and entitled "Multiplex receiving apparatus. i

The present invention, although not limited thereto, finds particular application to multiplex systems of the time division type. and for this reason the invention will be described with special regard thereto. In multiplex systems of the time division type the successive basic units of each.

channel are divided into equal portions of like number as the several-channels, and the transmitting circuit is assigned consecutively to suecessive channels for a time interval equal at most to one of these portions, the remaining portion of each basic unit of each channel being discarded and subsequently-restored at the receiving end of the circuit. 1 Such a multiplex arrangement is described in United States Patent No. 1,979,484, granted November 6, 19 34, to R. E. Mathes.

In brief, the present invention comprises a coupling system for assigning the received incoming signals to their respective channels, and for enabling the received signals to'be rebuilt to their original form as at the transmitting station, whereby the suppressed portions of the transmitted signals are restored. For effecting this purpose, use is made of a coupling electron discharge device whose normal condition of electrical stability is changed upon the'flow of signal currents in the input circuit of the receiving arrangement. 1 r

Referring to the single drawing accompanying this specification, there is shown a receiving cir- +Ee, .due to the 13 drop in resistance ll.

cuit arrangement for a multiplex system inaccordance with the present invention. This arrangement comprises, essentially, an energy 'collector or antenna L an amplifier and detector circuit 2 adapted to receive radio frequency 5 energy from the antenna and to detect same in a manner well known in the art, a tone keyer 3 under control of apparatus 2 for transmitting over a land line 4 to the receiving station audible frequency tone'which is interrupted in accordo ance with received signal energy, an amplifier and rectifier circuit I for producing the envelope oi' the keyed tone, coupling tube 6 and'so-called kicker arrangement I with associated apparatus for. assigning the incoming signals to their re- 15 spective channels, each of the channels having a locking circuit 28 for rebuilding the received signal and transmitting the restored signal to a suitable utilization circuit l8:

Amplifier-detector apparatus 2 and tone keyer go have been shown merely in conventional form since the manner of receiving signals over an antenna and subsequently amplifying and detecting the signals to operate a tone keyer is well known in the art. For a more detailed descrip-. 25 tion, however, of the operation of the tone keyer circuit reference is made'to United States Patent No. 1,874,866, granted to H. H. Beverage et al., particularly that portion which relates to Figure 2 thereof.

Similarly, amplifier-detector apparatus 5, which also is of a well known type, has been indicatedin box form, the output or iull wave rectiher part only being shown in order to illustrate its manner of connection to the coupling tube 8. Only ,the negative pulses of the rectified signal are applied to the grid of tube 6 since the positive end of the rectifier is tied down to the filament which is at ground or zero potential. A low pass filter 9 consisting of series inductance and shunt 40 capacitance is utilized for smoothing out whatever tone components remain in the rectified In the circuit diagram shown, coupling tube 6 is biased by means of a grid battery in to pass current normally, in which condition there exists a positive potential on its anode which is lower in value than the potential of the anode supply The to receipt of a signal pulse on the grid of tube 6, however, is arranged to bias the grid so negatively as to make the tube block, that is, cease passing current, at which time the voltage on the anode of tube I will rise to the maximum value of 1%, M

' since at this time substantially no current flows in the resistance I I.

Although this particular manner of operating tube 8 has been described, it will readily be understood that the invention is not limited thereto, since the desired coupling effect can be obtained in other ways. for example, by biasing tube 6 to. cut-oil at all times except when a signal is impressed on its grid, merely by the use of a reversing tube, or else by permitting tube I to draw current at all times and changing the magnitude thereof in accordance with the incoming signals.

when the incoming signals are applied to the grid of the tube 0 they, of course, vary the im- 7 pedance of the tube in such a way as to produce changes in thevoltage of the anode with respect to the cathode. These voltage changes are re- 5 is caused by the presence of a suitable potential I flected in corresponding variations of voltage drop across a resistor Lto a point A and further across a resistor it to a source ofdirect current potential the negative pole Eo of which is shown on the drawing to indicate a potential more negative than that of the cathode of the tube 0. The cathode is shown grounded but is not necessarily grounded. certain terminals 13 of a distributor or kicker arrangement. The distributor as shown in the 'drawing is provided with a kicker disc I which may consist of any suitable system of devices for conductively closing an.electrica1 circuit between different pairs of contact terminals or segments I! and I4. In a conventional type of distributor, for example, the segments I9 and II may be positioned on a common radius about the center of rotation of the element 1' and one or more brushes 12 may be caused to wipe over the stationary segments It, It so as to bridge the same. Each 0! the segments I4 is connected to an appropriate channel leading to a so-called locking circuit. The locking circuit for channel #I has been shown in detail, while that of channel #2 has been indicated by a legend. The operation of the distributor is such as to close a circuit. conductively to the locking circuits for the diiferent channels in succession. It will be understood that the distributor, although it is shown arranged for only two channels, may be adapted for any desired number 'of channels. This distributor is usually driven by a motor, not shown, which is maintained in synchronism by the incoming signals. The synchronizing means are, however, no part of the present invention. 1

In each receiving channel and in circuit with one of the contact segments ll of the distributor is a biasing resistor 19 leading to the negative biasing source Ee. The locking circuit includes two electron discharge devices It and H. The grid of tube It is directly connected to an appropriate distributor segment i4. Between this connection and the anode of tube I1 is a suitable resistor. A cross connection is also provided between the grid of tube I! and the anode of tube I. through a similar resistor. Other resistors are provided as shown in the drawing for biasing purposes and for causing the locking circuit to possess two 'altemative states of electrical stability. These tubes are unstable whenboth are drawing current, but stable when one tube is passing current and the other blocking. The

'changingfrom one condition of stable equilibrium, such as when tube it is blocking and tube I1 is passing, to the other condition, when tube II is passing and tube 11 blocking, or the reverse,

The circuit point A is connected to on the grid of tube I! which is due, in this case, to the polarity applied to segment ll of the distributor, and when it is bridged in contact with segment I! to receive either a positive or negative charge which for the moment appears at the point A due to the operation of the tube 8 and the consequent variation in the flow of current across resistor I. This locking circuit is more adequately described in United States Patent 1,844,950 granted February 16, 1932 to J. L. Finch,

to which reference is made for a more detailed explanation of the operation thereof.

Coupled to the output terminals of the locking circuit 28 may be any type of utilization circuit II, such as a relay, an ink recorder, a printer, or local tone oscillator. This utilization circuit responds to the changes of polarity occurring in the output of 29 for marking and spacing conditions which, in turn, are due to the unbalance of the locking circuit under its two degrees of stability.

The operation of the circuit is as follows: The respective values of the resistors II, I and i5 forming a potentiometer between the terminals +Es and E of the direct current source are suitably chosen for shifting the voltage of the point A above and below ground potential, depending upon the blocking condition or conductance of the tube 6. If this' tube is passing current the voltage at the point A is sufliciently negative with respect to ground so as to block the tube It when the distributor brush it applies this voltage to the grid of tube It. This condition having been established momentarily, the tube II will be excited to pass current and will continue to do so until a pulse of opposite polarity is introduced on the grid of the tube It. This change of polarity is occasioned by blocking tube 8 at the moment when a succeeding circuit is closed through the distributor to channel #I. Point A will now be positive with respect to ground so that the applied potential on the grid of tube It will be positive and will cause this tube to draw current, thereby cutting off the current flow in tube M.

It will be understood that various changes may be made in the resistance network such as will provide proper variations in the polarities at the point A with respect to ground so as to control each of the locking circuits in the multiplex system in the manner described. The essential feature of the system as shown is the provision of resistors having suitable values in relation to the biasing sources such that each locking circuit when connected through the distributor will be dependably controlled.

It will be noted that the particular circuit arrangement herein shown and described diifers considerably from that of my earlier invention as disclosed in United Stata Patent 1,995,181 since capacitive coupling means were there provided in place of resistive coupling means as herein shown. Furthermore, in the earlier invention of the patent the anode of tube I was directly connected to the segments ofthe distributor and the coupling means were interposed between the distributor and the locking circuit. In the present case, however, the coupling means-are interposed between the output circuit of the tube 8 and the distributor, and the distributor segments are directly connected to their respective locking circuits. These changes have been found to provide improved results and the novelty of the system is set forth in the appended claims. 7

1. A multiplex telegraph receiving system comprising an electronic circuit arrangement for'de- 1g ing two states of electrical stability under alter- 'native control of said signals when such are transferred thereto by said distributor, and a utilization circuit operable bychanges from one to the other of said states.-

2. A multiplex telegraph receiving system comprising an electron discharge tube under control of incoming signals, said tube having an output circuit connected from its anode through a resistor and a direct current source to its cathode, a multiplex distributor operative to connect said anode periodically to difierent channels, a second resistor interposed between said anode and said distributor, a third resistor connecting thev end of the second resistor adjacent the distributor to the negative pole of a direct current source whose positive pole is connected to said cathode, a signal storage device in each of said channels, and a utilization device connected to each said storage device and operative therefrom.

3. In a system for receiving telegraph signals by means of a multiplex channel distributor, a

plurality of locking circuits and a corresponding plurality of utilization devices, the -method or transferring said signals through the aforesaid apparatus units which comprises detecting and amplifying the signals, generating from said signals direct current impulses of difierent potentials, causing said impulses to be conductively transferred to and through said distributor and thence to each of said locking circuits in succession, and causing said locking circuits to prolong the effects of said impulses, thereby to control said utilization devices.

4. A multiplex telegraph receiving system comprising a signal responsive discharge tube, a direct current source and a resistor series connected across the discharge path of said tube, a plurality of locking circuits each appropriate to a communication channel in said system, a distributor having a plurality of channel segments each successively closeable to render said locking circuits individually responsive to signals applied to said discharge tube, a resistor connected between an output electrode of said discharge tube and a portion of said distributor common to the several channels, and means for producing a potential drop across the last said resistor which varies in dependence upon the conductive and non-conductive states of said tube, thereby to transfer said signals through said distributor to said locking circuits. A 

